In the semiconductor, electronics and life science industries viscous fluids are frequently dispensed. The demands to miniaturize in these industries require smaller and faster deposition of viscous fluids. Non-contact dispensing, often referred to as jet dispensing, is preferred for many reasons, some of which might be the ability to dispense drops while moving above a surface, the speed of drop formation, and the minute size and precision of the drops produced. Jetting as used herein refers to non-contact dispensing as compared to contact dispensing. Contact dispensing is the process where a fluid drop on the end of a dispensing tip comes into contact with the target substrate while still in contact with the dispensing tip so that the fluid drop “wets” or clings to the substrate and remains on the surface of the substrate as the dispensing tip pulls away. In the case of ink jet technology, inks with a viscosity very near water (<10 millipascal-seconds or mPas) are jetted. In the case of viscous jet technologies, fluids with high viscosities (>50 mPas) can be jetted. Examples of viscous fluids include adhesives, fluxes, oils, lubricants, conformal coatings, paints, slurries, UV inks, proteins, and enzymes.
As known in the industry, to produce a free flying jetted drop, energy must be imparted to the fluid which transfers enough momentum to force fluid through an orifice with the appropriate exit velocity for the fluid to break into a free flying drop. However, due to the different rheology of each fluid, the momentum transfer required and the resulting exit velocity to produce high-quality drops can be different. A high-quality drop of fluid as defined here is a drop that breaks-off cleanly (without satellite droplets separated from the main drop and without leaving behind residue that affects the succeeding drop volume or directionality) from the exit orifice and travels to the surface resulting in a single deposit of fluid on the surface. Given a specific amount of momentum transfer, one fluid can generate high-quality drops but a different fluid can generate poor quality drops, drops that accumulate on the nozzle tip or even fail to generate a drop. Poor quality drops could be caused by small “satellite” droplets that separate from the main drop and form multiple deposits on the surface. Or, poor quality drops could be a result of excessively high exit velocity of the drop which can hit the surface and form splattered droplets surrounding the main drop. In both cases, the resulting jetted drop would not be considered high-quality, nor would the failure to generate an expected drop be considered high-quality. Other measures of high-quality drops could be the repeatability of the drop size, shape of the drop, or other measures. There is thus a need for a method and apparatus to precisely measure, adjust, and control the transfer of momentum to the fluid, and/or the resulting drop exit velocity that would be beneficial for producing repeatable, high-quality jetted drops of viscous fluid. Advantageously, the fluid has a viscosity of greater than about 50 mPas, and more preferably a viscosity of over 150 mPas.
Non-contact jets generally have specific construction which either restricts the flow of material through the exit orifice in the power-off state, a normally-closed construction, or allows the flow of material through the orifice in the power-off state, a normally open construction. Jetting high-viscosity fluid using a flexible diaphragm is known and described in U.S. patent application 61/293,837 and U.S. Pat. No. 5,320,250. A flexible diaphragm is preferred for many reasons, some of which might be the lack of dynamic fluid seals and ease of cleaning. However, the normally-open construction can allow the fluid to drip from the orifice when the power to the jet is shut off which can cause a loss of fluid and require the time and expense of clean up. There is thus a need for a method and apparatus to close the fluid path automatically when the power is shut off.
When jetting fluid with a flexible diaphragm, the diaphragm material should be chemically compatible with the fluid being jetted. Some chemically aggressive fluids can have an adverse effect on an elastomeric diaphragm usually noted by swelling of the diaphragm material. If swelling occurs, the diaphragm can deflect into the jetting chamber and restrict the flow of fluid into the jetting chamber or to reduce the chamber volume. If flow is restricted or the chamber volume reduced, the quality of the jetted drop can be adversely affected. There is thus a need for a way to determine if the diaphragm material has swollen and has deflected into the jetting chamber. Additionally, the overall life of the diaphragm can be compromised by swelling. There are chemically inert materials that can be used as a diaphragm; however, the cost of these chemically inert materials can be very expensive. There is thus a need for a way to use a low-cost diaphragm material with aggressive fluids and to also minimize the effect of swelling.